Locomotives generally use an internal combustion engine to drive a power source, such as a generator or an alternator, to propel a train. Such generators or alternators may convert a mechanical energy of the internal combustion engine into electrical energy (or power) and energize a set of traction motors of the locomotive. The traction motors in turn drive a set of locomotive wheels, thereby enabling locomotive propulsion.
Trains, including passenger trains typically require electrical power for powering various applications that may be unrelated to locomotive propulsion. For example, some locomotives may include an auxiliary power locomotive (APL) system that may provide electrical power for heating, cooling, ambient lighting, and energizing various electrical outlets of the locomotives, and a head end power (HEP) system that may be configured to provide electrical power for heating, cooling, ambient lighting, and energizing various electrical outlets for the railcars of the trains.
During locomotive retardation or braking, a dynamic brake mode may be applied in such locomotives. In a dynamic brake mode, regenerative energy is generally generated by the traction motors. Such regenerative energy may be dumped into one or more dynamic brake (DB) grids of the braking system, and/or the regenerative energy may be consumed by the HEP system and APL system. However, because a resistance provided by the DB grid is generally of a fixed value, a voltage developed across an associated DC link may drop as power dissipated across the DB grid drops. As a result, the alternator may require to support a steady DC link voltage, and may thus need the internal combustion engine to provide supplementary power, leading to a consumption of fuel in the dynamic braking mode.
German Patent DE102009054785A1 relates to a braking chopper that has a three-phase power inverter module that is linked at the direct current side with connectors of an intermediate voltage circuit and is linked at the alternative current side with resistances. The power inverter module has three bridge sections with two electrical semiconductor switches, whose connection points form the alternative current sided connections of the power inverter. Free ends of the resistances are linked together.